Selected Quarterly Financial Data (Unaudited) - (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Apr. 30, 2017	Jan. 31, 2017	Oct. 31, 2016	Jul. 31, 2016	Apr. 30, 2016	Jan. 31, 2016	Oct. 31, 2015	Jul. 31, 2015	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Selected Quarterly Financial Data (Unaudited)
Net sales	$ 614,977	$ 562,523	$ 591,846	$ 549,800	$ 527,182	$ 420,482	$ 458,077	$ 452,441	$ 2,319,146	$ 1,858,182	$ 1,570,085
Gross profit	201,035	185,727	193,224	178,585	174,203	134,160	143,913	140,888	758,571	593,164	478,971
Net income (loss)	$ 14,273	$ 8,226	$ 17,224	$ 9,163	$ 8,940	$ (2,212)	$ 2,825	$ 3,011	$ 48,886	$ 12,564	$ (11,697)
Weighted average shares outstanding:
Basic (in shares)	40,955,632	40,942,905	40,942,905	38,200,597	32,892,905	32,890,930	32,737,956	32,677,418	40,260,405	32,799,098	32,450,401
Diluted (in shares)	41,758,974	41,577,675	41,319,651	38,602,378	33,155,140	32,890,930	32,898,075	32,830,677	41,070,025	33,125,242	32,450,401
Net income (loss) per share:
Basic (in dollars per share)	$ 0.35	$ 0.20	$ 0.42	$ 0.24	$ 0.27	$ (0.07)	$ 0.09	$ 0.09	$ 1.21	$ 0.38	$ (0.36)
Diluted (in dollars per share)	$ 0.33	$ 0.20	$ 0.42	$ 0.24	$ 0.27	$ (0.07)	$ 0.09	$ 0.09	$ 1.19	$ 0.38	$ (0.36)